This invention relates to expansible chamber energy conversion machines and more particularly, it concerns a novel apparatus for varying the stroke of a reciprocable piston in such machines without substantial variation in the volumetric ratio of the expansible chamber defined in part by the piston.
Expansible chamber energy conversion machines typically include Otto or Diesel cycle internal combustion engines, heat engines in which fuel is burned externally, such as steam engines and Stirling engines, air motors, as well as machines which operate to transform mechanical energy to fluid and/or thermal energy, such as compressors and pumps. In all such machines, operating efficiency is optimized when the work performed in the expansible chamber is correlated with the load demand for converted energy. Where the energy conversion requirements are widely variable therefore, variation in the volumetric capacity of the expansible chamber is significant in the attainment of optimum efficiency under all operating conditions.
In a co-pending application for U.S. Pat. Ser. No. 738,704 filed Nov. 3, 1976 by Yves Jean Kemper and assigned to the assignee of the present invention, there is disclosed as embodiment of an internal combustion engine in which power developed by pistons reciprocating in cylindrical combustion chambers in transmitted to a nutating generally cylindrical member carried by an external rotary support member about an output shaft having a pair of oppositely convergent cone-like members to which torque is transmitted by friction from internal rolling surfaces on the cylindrical nutating member. The thrust of piston reciprocation is absorbed by double-ended swivel links each having one end universally pivotal about a fixed point of reference and the other end universally pivotal in a socket fixed at one end of the nutating cylindrical member. A feature of the illustrative embodiment disclosed is the provision of an eccentric sleeve means by which the angle of cylindrical member nutation may be varied in a manner to vary the length of piston stroke relative to a cylinder head either with or without a constant compression ratio.
In the engine disclosed in the aforementioned application, the frequency of piston reciprocation is directly proportional to the angular velocity of the support journaled to the exterior of the cylindrical nutating member. Output speed or angular velocity of the shaft to which the cone-like members are keyed is a function of the effective internal radius of the nutating cylindrical member and the radii of the cone-like members at the point of frictional engagement between these members. Output speed may be varied for a given engine speed by shifting a pair of ring-like members carried on the interior of the cylindrical nutating member axially of the cone-like members carried on the output shaft.
In another co-pending application for U.S. Pat. Ser. No. 743,600, filed Nov. 22, 1976 by Yves Jean Kemper and also commonly assigned with the present invention, there is disclosed a piston engine in which the output shaft speed of the engine is varied in inverse proportion to piston stroke length variation in response to an adjustable control function determinative of both piston stroke length and the ratio of engine speed to output shaft speed. This operating characteristic is achieved by a similar structural arrangement in which a pair of cone-like members, rotatably supported on a first axis, are driven by rolling friction engagement with cylindrical interior rolling surfaces of a nutatable member having a second axis inclined with respect to and intersecting the first axis midway between the cone-like members. The nutating member is also supported externally by a support member journaled for rotation about the first axis in direct proportion to engine speed or frequency of piston reciprocation but in the disclosure of this latter application, torque developed in the support member is transmitted as one of two inputs to an epicyclic gear train, the other of the two inputs being a direct connection with the cone-like members. These torque inputs are transmitted through the epicyclic gear train to a common engine output shaft.
Further in accordance with the disclosure of Ser. No. 743,600, variation in piston stroke length as well as speed variation of torque transmission to the cone-like members is effected by adjusting the angle of first and second axes intersection, again using an eccentric sleeve provided between the exterior of the nutating cylindrical member and the support member. In this instance, the cone-like members are designed with a long meridianal radius so that variation in the angle of first and second axes intersection will shift the points of rolling friction contact between the interior of the nutating cylindrical member and the cone-like members along the axial length of the cone-like members and correspondingly, vary the effective radius of the cone-like members. As a result, engine speed, piston stroke and output shaft speed are correlated in a manner to optimize operating efficiency.
In the machines disclosed in both of the aforementioned co-pending applications, piston connection with the nutating member is by way of rigid arm-like extensions of the nutating member, the thrust of piston force being absorbed by double-ended swivel links or "dog bones", as they are sometimes referred to in the art, each having one end swivelled in the machine frame at a fixed fulcrum point and the other end swivelled at the juncture of the arm-like extension and the nutating member. As a result of this construction, variation in the angle of intersection between the axis of the nutating member and the axis of the conical members results in an axial shifting of the nutating member, its support and the conical members, a feature which is required to maintain the various machine components in a balanced state of the equilibrium and also which is advantageously deployed to achieve variations in piston stroke length with a predictable variation in compression ratio where cylinder heads are fixed to the frame.
While the machines disclosed in the aforementioned co-pending patent applications represent a significant advance in the art, there is need for improvement principally from the standpoint of increasing the range of piston stroke variation in a given machine design. In addition, the achievement of adequate strength in the connection of the pistons to the nutating member using curved arm-like extensions presents problems both from the standpoint of manufacturing difficulty and likelihood of failure due to metal fatigue in operation over extended durations of time.